Running angle

In mathematics, the running angle is the angle of consecutive vectors $$(Xt,Yt)$$ with respect to the base line, i.e.
 * $$\phi(t) = \arctan\left(\frac {\Delta Yt} {\Delta Xt} \right) .$$

Usually, it is more informative to compute it using a four-quadrant version of the arctan function in a mathematical software library.